**Abstract**

In this study, the effect of Al2O3 with various volume percentages in annular fuels for a typical VVER-1000 core is investigated. CFD is used to simulate the fuel rod. The results of the present study are compared with those of other published studies. Furthermore, the mentioned analytical methods are validated by comparing the final safety analysis report (FSAR). By comparing the results, it was found that the results are in good agreement with other studies. The results show that using annular fuel instead of solid fuel in the core of the reactor will increase the security and efficiency of the nuclear power plant. By increasing the volumetric concentration of nanofluid from 0.1 to 0.2, the rate in decrease of the peak temperature in the central fuel increases from 9% to 13%. Moreover, the clad temperature decreases from 626 K to 620 K (the clad temperature with pure water is 635 K).

**Keywords:** annular fuel, nanofluid, VVER-1000, heat transfer, coolant
